1. Field of the Invention
The present invention relates to a circuit voltage regulator.
2. Description of the Related Art
FIG. 2 is a block diagram showing a configuration example of a conventional voltage regulator. A source terminal and a drain terminal of a P-channel MOS transistor 1 are connected in series between an input terminal 101 and an output terminal 103. A gate terminal of the P-channel MOS transistor 1 is connected with an output terminal of a differential amplifying circuit 10. Respective input terminals of the differential amplifying circuit 10 are connected with an output voltage terminal of a reference voltage source 11 and an output voltage terminal of a voltage dividing circuit 12.
The differential amplifying circuit 10 compares a voltage of the reference voltage source 11 with an output voltage of the voltage dividing circuit 12, keeps the voltage of the output voltage terminal of the reference voltage source 11 and the voltage of the output voltage terminal of the voltage dividing circuit 12 to the same voltage, and controls a gate voltage of the P-channel MOS transistor 1 so as to keep a voltage of the output terminal 103 to be a predetermined value.
In order to limit a current value in the case where the output terminal 103 of the voltage regulator is short-circuited and to prevent the P-channel MOS transistor 1 from overheating, a P-channel MOS transistor 2 having a gate terminal and a source terminal which are common to the gate terminal and the source terminal of the P-channel MOS transistor 1, a resistor 21 inserted between the output terminal and the drain terminal of the P-channel MOS transistor 2, a resistor 22 connected with the input terminal 101, and an N-channel MOS transistor 3 in which the drain terminal is connected with the resistor 22 in series are provided. The output terminal 103 is connected with the drain terminal of the N-channel MOS transistor 3. The gate terminal of the N-channel MOS transistor 3 is connected with the drain terminal of the P-channel MOS transistor 2. A base terminal of the N-channel MOS transistor 3 is connected with a ground terminal 102. The drain terminal of the N-channel MOS transistor 3 is connected with a gate terminal of a P-channel MOS transistor 4. A source terminal of the P-channel MOS transistor 4 is connected with the input terminal 101. The drain terminal of the P-channel MOS transistor 4 is connected with the gate terminal of the P-channel MOS transistor 1.
When a current flows into the P-channel MOS transistor 1, a current flows into the P-channel MOS transistor 2 based on a ratio determined by a ratio of a channel length and a channel width with respect to the P-channel MOS transistor 1 and the P-channel MOS transistor 2.
A voltage between both ends of the resistor 21 is inputted to an invert circuit composed of the resistor 22 and the N-channel MOS transistor 3 and the output of the invert circuit is inputted to the gate of the P-channel MOS transistor 4 inserted between the gate and the source of the P-channel MOS transistor 1 so that the P-channel MOS transistor 4 is turned ON/OFF. Thus, a voltage between the gate and the source of the P-channel MOS transistor 1 can be adjusted so that a value of a current flowing into the output terminal 103 can be controlled to a specified value.
Next, circuit operation will be described. If the output terminal 103 is short-circuited with the ground terminal 102, a large current tends to flow into the P-channel MOS transistor 1. At this time, a current which is determined by a ratio of a channel length and a channel width with respect to the P-channel MOS transistor 1 and the P-channel MOS transistor 2 flows into the P-channel MOS transistor 2. The voltage between both ends of the resistor 21 is risen proportional to the current value. When the voltage exceeds a threshold voltage of the N-channel MOS transistor 3, the N-channel MOS transistor 3 is turned ON and a voltage between the gate and the source of the P-channel MOS transistor 4 is increased. Thus, the P-channel MOS transistor 4 tends toward an ON state.
If the P-channel MOS transistor 4 is shifted toward an ON state, a gate voltage of the P-channel MOS transistor 1 approaches a potential of the input terminal 101. Thus, a voltage between the gate and the source of the P-channel MOS transistor 1 becomes smaller so that it is shifted toward an OFF state. By such operation, a current flowing into the P-channel MOS transistor 1 is limited and decreased.
FIG. 3 shows a characteristic between an output current flowing into the output terminal 103 and an output current at this time. As shown in FIG. 3, the output current is reduced from a maximum current Im as the output voltage is reduced. Then, when the output voltage is zero, that is, the output terminal 103 is short-circuited with the ground terminal 102, it becomes a current value of shirt circuit current Is. A mechanism by which this characteristic is realized is obtained due to the fact that a source potential of the N-channel MOS transistor 3 is different from a base potential so that a threshold voltage of the N-channel MOS transistor 3 is varied by a back gate effect. When the output voltage of the voltage regulator is reduced, the threshold voltage of the N-channel MOS transistor 3 becomes lower by a back gate effect.
When the threshold voltage of the N-channel MOS transistor 3 becomes lower by a back gate effect, even if a current flowing into the resister 21 is small, the N-channel MOS transistor 3 is turned ON. Thus, a current flowing into the P-channel MOS transistor 1 becomes smaller. Accordingly, a characteristic as shown in FIG. 3 is obtained, which is expressed by a fixed straight line and subsequent turn-back slant line (for example, see patent reference 1).
Patent Reference: JP 07-74976 B (FIGS. 1 and 3)
The maximum current Im is a current used in a device connected with the output terminal 103. Thus, it is required that this current is maximized. In addition, a short circuit current Is is a current produced at a time when the output terminal is short-circuited with the ground terminal. Thus, it is required that this current is minimized.
However, according to the voltage regulator having the above configuration, a ratio of Im and Is is dependent on a back gate effect of the N-channel MOS transistor 3. Thus, the ratio of the maximum current Im and the short circuit current Is of the voltage regulator can not be adjusted. Accordingly, there is a problem that the maximum current cannot be made large and the short circuit current cannot be made small.
In order to solve the above-mentioned problem, according to a voltage regulator of the present invention, the configuration is used in which a resistance value for detecting an output current is changed by an output voltage and a limited current can be changed according to the output voltage.
Therefore, according to the invention of the present application, there is provided a voltage regulator for controlling a current flowing into an output voltage terminal in accordance with an output voltage, comprising:
a first MOS transistor having a first conductivity type in which a source terminal thereof is connected with an input voltage terminal and a drain terminal thereof is connected with the output voltage terminal;
a differential amplifying circuit having two input terminals in which an output terminal thereof is connected with a gate terminal of the first MOS transistor;
a first reference voltage source which is connected between one of the input terminals of the differential amplifying circuit and a ground terminal and in which an output terminal thereof is connected with the one input terminal of the differential amplifying circuit; and
a voltage dividing circuit which is connected between the output voltage terminal and the ground terminal and in which an output voltage terminal thereof is connected with the other input terminal of the differential amplifying circuit.
The voltage regulator of the present invention further comprises:
a second MOS transistor having the first conductivity type in which a gate terminal and a source terminal thereof are connected with the gate terminal and the source terminal of the first MOS transistor, which are common to each other, respectively; and
a first resistor connected between the output voltage terminal and a drain terminal of the second MOS transistor.
The voltage regulator of the present invention further comprises:
an MOS transistor having a second conductivity type in which a source terminal thereof is connected with the output voltage terminal, a gate terminal thereof is connected with the drain terminal of the second MOS transistor, and a base terminal thereof is connected with the ground terminal; and
a second resistor connected between the input voltage terminal and a drain terminal of the MOS transistor having the second conductivity type.
The voltage regulator of the present invention further comprises:
a third MOS transistor having the first conductivity type in which a source terminal thereof is connected with the input voltage terminal, a gate terminal thereof is connected with the drain terminal of the MOS transistor having the second conductivity type, and a drain terminal thereof is connected with the gate terminal of the first MOS transistor;
a third resistor connected between the first resistor and the output voltage terminal; and
a fourth MOS transistor having the first conductivity type in which a drain terminal and a source terminal thereof are connected with the third resistor in parallel.
Further, the voltage regulator of the present invention is characterized in that a voltage of a gate terminal of the fourth MOS transistor is a voltage lower than a specified output voltage.
Further, there is provided a voltage regulator according to a first aspect of the present invention, characterized in that the gate terminal of the fourth MOS transistor is connected with the ground terminal.
Further, there is provided a voltage regulator, characterized in that the gate terminal of the fourth MOS transistor is connected with the output terminal of the voltage dividing circuit.
Further, there is provided a voltage regulator further comprising a second reference voltage source in which a reference voltage (V1) lower than a specified output voltage is set, characterized in that the gate terminal of the fourth MOS transistor is connected with the second reference voltage source.
Further, according to the invention of the present application, there is provided a voltage regulator for controlling a current flowing into an output voltage terminal in accordance with an output voltage, comprising a first MOS transistor having a first conductivity type in which a source terminal thereof is connected with an input voltage terminal and a drain terminal thereof is connected with the output voltage terminal.
The voltage regulator of the present invention further comprises:
a voltage dividing circuit connected between a ground terminal and the output voltage terminal;
a reference voltage source;
a differential amplifying circuit in which an output terminal thereof is connected with a gate terminal of the first MOS transistor and two input terminals thereof are connected with an output terminal of the reference voltage source and an output voltage terminal of the voltage dividing circuit, respectively;
a first current limiting circuit for limiting a current value of the output voltage terminal; and
a voltage detector for detecting a reduction in voltage of the output voltage terminal.
The voltage regulator of the present invention is characterized by further comprising:
a second current limiting circuit for limiting a current value of the output voltage terminal to a limited current value or smaller of the first current limiting circuit; and
a switch element for switching from the first current limiting circuit to the second current limiting circuit when the voltage of the output voltage terminal which is detected by the voltage detector is a specified voltage or lower.
Further, the second current limiting circuit includes:
a second MOS transistor having the first conductivity type in which a source terminal and a gate terminal thereof are connected with the input voltage terminal and the output terminal of the differential amplifying circuit, respectively; and
a third MOS transistor having the first conductivity type in which a source terminal, a drain terminal, and a base terminal thereof are connected with the input voltage terminal, the output terminal of the differential amplifying circuit, and the ground terminal, respectively.
The second current limiting circuit further includes:
an MOS transistor having a second conductivity type in which a source terminal, a gate terminal, and a drain terminal thereof are connected with the output voltage terminal, the drain terminal of the second MOS transistor, and a gate terminal of the third MOS transistor, respectively;
first and third resistors connected in series between the drain terminal of the second MOS transistor and the output voltage terminal, the first resistor being connected with a drain terminal of the second MOS transistor; and
a second resistor connected between the input voltage terminal and the gate terminal of the third MOS transistor.
Further, the present invention is characterized in that the switch element is connected with the third resistor in series, and that the first current limiting circuit corresponds to the second current limiting circuit produced by short-circuiting the third resistor by the switch element.
Further, the switch element includes a fourth MOS transistor having the first conductivity type. A drain terminal and a source terminal of the fourth MOS transistor are connected with the output voltage terminal and the first resistor, respectively. Further, the present invention is characterized in that:
the voltage detector includes a voltage comparator and a reference voltage source;
the reference voltage source is connected with the ground terminal;
two input terminals of the voltage comparator are connected with the reference voltage source and the output voltage terminal, respectively; and
an output terminal of the voltage comparator is connected with a gate terminal of the fourth MOS transistor.
Further, a voltage regulator according to the present invention is characterized in that a base terminal of the MOS transistor having the second conductivity type is connected with the output voltage terminal.
Further, a voltage regulator according to the present invention is characterized in that:
the source terminal and the base terminal of the MOS transistor having the second conductivity type are connected with the ground terminal; and
the first and third resistors are connected in series between the ground terminal and the drain terminal of the second MOS transistor.
Further, according to the present invention, there is provided a voltage regulator, comprising:
an input terminal to which an input voltage is applied;
an output terminal from which an output voltage is outputted;
a ground terminal;
a voltage detecting circuit for outputting a voltage detection signal in response to a signal of the output terminal;
a voltage dividing circuit for dividing a voltage between the output terminal and the ground terminal;
a reference voltage source;
a differential amplifying circuit for outputting a signal in response to an output of the voltage dividing circuit and an output of the reference voltage source; and
a resistor circuit in which a resistance is changed in response to the voltage detection signal from the voltage detecting circuit.
The voltage regulator of the present invention further comprises:
a first current limiting circuit in which an input is connected with the input terminal and an output is connected with the resistor circuit and which is controlled in response to an output of the differential amplifying circuit, the resistor circuit being connected between the first current limiting circuit and the output terminal; and
a second current limiting circuit in which an input is connected with the input terminal and an output is connected with the output terminal and which is controlled in response to the output of the differential amplifying circuit.
Further, the voltage regulator of the present invention is characterized in that the resistor circuit includes:
an invert circuit for outputting a signal in response to an output of the first current limiting circuit; and
a switch element which is connected between the input terminal and the differential amplifying circuit and controlled in response to an output of the invert circuit.